The present invention relates to a method of producing non-abrasive coke forms from brown-coal briquets, according to which the briquets are preheated, dehydrated, carbonized and subsequently cooled, with the entire operation being effected in at least three stages and with the use of hot gas circuits in which the hot gas is composed substantially of the burnt lean gas of the carbonization or low temperature carbonization process.
Such method is well known in the art. Frequently the individual stages are united or merged into one another. While a complete separation of the individual stages is technically very difficult to achieve, in view of a better utilization of the circulating hot gases, a complete separation of the hot gas circuits would be desirable. The technology also seeks to increase the mechanical resistance of the produced coke forms. Particular difficulties result from the fact that, in their circulation, the hot gases carry along large quantities of coal dust originating in the abrasion of the briquets and, at the same time, containing oil and tar components. This entails particular problems of condensation which, up to date, have not been solved in the art in a satisfactory manner. In this respect again, an increased mechanical resistance of the briquets to be coked is desirable.
German Pat. No. 530,983 describes a process where pressure-resistant solid coke is obtained from lignites and the like by a two-stage distillation, and where the material traversing the oven in counter flow is evened by scavenging gases and brought, in the second stage, abruptly from about 450.degree. C. to about 700.degree.-1,000.degree. C.
German Pat. No. 882,392 describes a process for the continuous distillation of hard coal briquettes and a low-temperature carbonization or a high-temperature coking stage with exclusive heating of both stages by directly acting heated gases, where the distillation gases produced separately in each stage are kept in circulation by constant reheating. However, this patent contains no information on the production of the briquettes, particularly on whether caking coal or non-caking coal was used.
British Pat. No. 947,726 describes a counter flow method for coking lumpy Australian brown coal to lumped coke, where thecoal is preheated in a drying and preheating zone to about 200.degree.-300.degree. C. and fed to a low-temperature coking zone heated with hot gases in which each following stage has a higher temperature than the preceding stage, and the maximum temperature difference between the gas and the material to be coked does not exceed 150.degree. C. at the outlet of the stage, and is then completely coked in a high temperature zone.
U.S. Pat. No. 3,018,227 concerns a process where briquettes, compressed from special coal mixtures and with the addition of pitch, are coked to shaped coke pieces, and the briquettes are subjected to a temperature shock with their surfaces being heated spontaneously to 532.degree.-677.degree. C.
Berry U.S. Pat. No. 2,131,702 describes a process for continuous coking, where coal briquettes from caking coal are heated to such an extent in a first zone that degasificatio starts, and heated in a second zone from the softening temperature to 500.degree.-600.degree. C., and then heated in a third zone to 700.degree.-1,000.degree. C.
These known methods can be used for coking lumped coal of a certain type and for briquettes which were produced from a certain type of coal and in a certain manner. However, a general solution of the problem of coking briquettes from brown coal with lower coking qualities, particularly from non-caking brown coal, has not yet been suggested.
Since workable deposits of caking brown coal, which imparts good coking property to the briquettes produced therefrom, and from which shaped coke pieces of sufficient strength and hardness for metallurgical use have become rare, the industry still faces the problem of briquetting brown coals with lower coking qualities, that is, non-caking brown coals, and of producing coke therefrom. The solution of this problem is aggravated by the fact that these coals must be briquetted, in most cases for economical reasons, without the addition of binders.
The condensation and scrubbing of oil and tar components out from the dust-laden gases leads to the necessity of removing the washing lquids, which are loaded with coal dust, from the scrubbing circuit, since their viscosity becomes excessive and they can no longer be pumped. The further processing of such mixtures is expensive wherefore a better dust separation from the circulating gases would represent a technological progress, all the more as the dust entrained by the circulating gases causes clogging in almost all parts of the equipment, and which can be cleared only by troublesome manual work.
In known methods, temperatures of 110.degree. C. to 135.degree. C. for the preheating, 230.degree. C. to 330.degree. C. for the drying and 550.degree. C. to 650.degree. C. for the coking are used.
It is also known to use the lean gas, produced during the carbonization, for preheating and drying and as the drying gas for preheating and subsequently, to evacuate the gases into the free atmosphere. It is also known to separate the individual stages by means of mechanical members, such as lids. However, this measure frequently entails disturbances in the plant.